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Matco Bleeding Problem (on a conversion)


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I had an issue getting my matco calipers to bleed. I could not push 5606 into the bleed nipple. Figured it was a piston problem, but I wanted to check with Roger and Matco first. Roger suspected what Matco confirmed, the piston was driven too far back. According to Matco, the pistons are flat on the backside, and if they are driven back all the way and there's no fluid, they can seat and it takes a lot of pressure to get them to move again, something that a little hand bleeder can't do.

 

I was going to run 5606 from the reservoir and bleed it from the brake line fitting, then use the master cylinder to drive pressure to unseat it. Both Roger and Matco offered an alternative idea: use shop air. As a note: Matco said to have the rotor and linings in place so the piston doesn't get blown clean out. So I grabbed a hose, put a rubber end on, and sealed it tightly against the brake line side of the caliper. It took a second or so, but then I heard a "pop" and noticed the pad seated against the rotor. Did that to both calipers, then pushed red oil into the system very easily!

 

To make sure I purged all the air out of the freshly installed system, I started by filling from the left caliper right up until I saw red oil starting to come out of the reservoir side of the master cylinder. I closed the bleed, I switched to the right caliper, and pumped until the reservoir almost overflowed. I closed up and sealed the right caliper (there won't be any air getting in that line now), then went back to the left caliper, opened the bleed again. pumped the master cylinder a couple times (that's about all it takes to nearly empty the reservoir), then pushed red oil back from the caliper. I had to do this a couple more times on the left to make sure all residual air bubbles got out, and now the brakes are solid and firm.

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They were installed when I did it. The pistons are pretty large on these things (little over 2 inch diameter?), so any input pressure is multiplied 3-4 times. At a hundred PSI input pressure, that will be enough to really mess up my day if I had my hands anywhere near those liners.

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The best way would have been to attach a line to the top of the reservoir back to the hand pump. Then I could have just pumped all day. The emptying and pumping back in takes time. I had to do it that couple extra times because I pulled one too many times on the handle and it sucked air.

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So I did my break-in run for the brakes. Rode those brakes all 5000 feet at 3500 rpm on the runway, periodically giving them a slow down pull. Got back to the hangar, they were hot enough that touching the rotor briefly resulted in a mild burn.

 

After cooldown, went back out and hit the parking break, warmed up, and gunned to 5,000 RPM briefly. No movement. Released, went back out on the runway, went up to 50 kts, and pulled. Realized real quick that it takes a lot less force to skid the tires with Matco than it did with the Marc wheels!

 

Now to make the logbook entries so I can do the flight test!

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